Emerging from a four-month struggle with cancer, Republican National Committee Chairman Lee Atwater said yesterday he is "back in the act" and has been urging party leaders and the White House to "go on the offensive and be more aggressive" in challenging Democrats on issues ranging from the savings and loan scandal to tax increases.

As the Republican National Committee (RNC) convened in Chicago yesterday for its second major session since Atwater was discovered to be suffering from a brain tumor in March, the chairman scoffed at growing concerns among some party leaders that the White House has lost its political edge in his absence.

"If I were right there on the job, somebody would say I was screwing up or you can't run White House politics out of my office," he said during two telephone interviews this week. Displaying uncharacteristic humility, he added, "I seem to look a lot smarter and a lot better when I'm gone."

Atwater said his doctors believe the radical radiation therapy he underwent in April has been successful in stopping the aggressive growth of the tumor and causing it to begin to recede. But many of the medical problems associated with the cancer remain, preventing Atwater from resuming anything like the schedule he had before his illness.

He has not appeared in public since March and probably will not for at least a few weeks, robbing the party of what RNC chief of staff Mary Matalin calls its "most visible partisan voice." He was hospitalized Thursday with problems related to the medication he is taking, but he said yesterday it was "just part of the routine" and that he feels well.

"He can walk but he can't run," said Paul Kornblith, the New York physician overseeing Atwater's treatment. That assessment of Atwater's physical condition also could serve as a description of his expanding but still curtailed role in party and White House politics.

GOP and White House officials said in interviews this week that Atwater is beginning to participate in a more organized fashion with the White House on pending political issues, particularly sensitive ones such as President Bush's decision to abandon his "no-new-taxes" campaign pledge and what Atwater called the "Democrat strategy to try to politicize" the S&L crisis.

Atwater said he has strongly urged the White House to avoid a tax package that would include personal income tax rate increases so that Bush can retain "some purity at least" on his campaign pledge. The effect on the party and the president of tax increases, he said, "will not be helpful in the short term, but I think won't be very damaging in the long run, particularly if the Democrats are all standing on the same line together and it's not a personal income tax increase."

The RNC chairman also expressed alarm at the Democrats' ability to put the administration on the defensive over the thrift collapse. Listing Democrats caught up in the scandal, he said, "If we are stupid enough to get put on the defensive over this, we deserve what we get. You can't play defense in this game. I have played offense in politics for 20 years and that's the way you win."

Atwater insisted the White House did not mishandle the politics of the tax issue but many GOP officials and others cite it as a prime example of dulled political instincts. Bush's willingness to accept higher taxes was announced without advance warning to Republican candidates and key GOP members of Congress and then the president holed up in silence, allowing Democrats to shape the public debate.

While White House and party officials insist that Atwater's absence has not created a major vacuum, others strongly disagree. "You don't have a 'let's-make-things-happen' attitude without Lee," one activist said.

Some steps have been taken in recent weeks to firm up the political apparatus and "get us back in fighting shape," said one official of an internal reorganization that shifted responsibility for politics directly under the control of White House Chief of Staff John H. Sununu.

Sununu has named a deputy, Edward Rogers, as the de facto White House political director, making him the key link between the GOP political community, the party apparatus and the White House. Rogers, who is one of Atwater's closest friends, said his role will be to inject "what is happening politically, the political significance" of the day's events into day-to-day White House operations.

Atwater, in a discussion that ranged from local political races to the impact of national issues such as taxes and the thrift collapse, was noticeably subdued in comments about individual Democrats. His battle with cancer, he said, has given him "a different outlook. I look forward to being more issue oriented. I don't plan to attack on the personal basis to the extent I used to. I'm going to cool my jets a little bit on personalities."

An Atwater friend this week said the RNC chairman has made clear in private that the aggressive, street fighting, often personal kind of politics he has practiced for two decades will be tempered. "He will never be the Lee you knew," said the friend. "That edge will never be there again. He is not the angry young man who has to prove himself. He is now a young man who wants to live to be an old man."

Atwater made his first appearance at his office at the RNC last week and conducted an hour-long strategy session. Most of his work, he said, is done by phone and by memo. He has dictated a stream of strategy and tactical memos in recent days to Matalin and the White House, and has begun holding "drive-around" strategy sessions with his aides in his car.

He still uses a wheelchair, although he has made some progress in walking. His left side, once virtually paralyzed, has begun to respond to daily therapy sessions, and his hair has begun to grow back after chemotherapy. Continuing treatment and its aftereffects still consume huge chunks of his energy and time.

But associates said that preoccupation with his health is receding and Atwater's lifelong passion for politics is reemerging. "I feel better, I love politics and I'm spending more and more time at it," Atwater said.

Kornblith and others acknowledged that a major problem with Atwater's type of cancer is that it often recurs when "renegade" cells emerge months or years after treatment. For that reason, Kornblith said, "I can say the treatment is successful but I have treated many patients with this problem and I never use the word" cure. Atwater will have to be monitored "all his life."

Atwater said he understands the uncertainty of his health. "You take life one day at a time," he said. "That garbage truck can run over one person as soon as another. As long as a day goes by and I am here to see the next one, I am a happy man."

Staff writer Dan Balz contributed to this report.